1. Field of the Invention
The present invention relates to battery systems and, more particularly, to a battery system adapted for use at varying temperatures.
2. Description of the Prior Art
Present lithium-ion (Li-ion) cells demonstrate low operating efficiency, and a corresponding low discharge capacity, at temperatures below 20xc2x0 C. While a Li-ion cell may demonstrate a low discharge capacity at a low temperature, it will recover to a normal discharge capacity when the ambient temperature returns to a higher value.
Li-ion cells generate heat during discharge. Therefore, insulating a Li-ion cell during use at low temperatures causes the cell to demonstrate a higher discharge capacity than if it were uninsulated. However, maintaining the insulation on the cell when the cell is used in a higher temperature environment could have negative effects on the cell because of excess accumulation of heat.
Therefore, there is a need for an apparatus that retains heat in Li-ion cells while operating at relatively low temperatures, and that conducts heat from the cells while operating at higher temperatures.